The present invention emerged from ongoing research activity since 1957. In the late 1950's, the present inventor made oil-in-water emulsions using components such as cetyl palmitate, glycerol monostearate, soap, mineral oil, water dispersible gums and spermacetti (obtained from the sperm whale) as thickeners. The inventor also used thickeners such as paraffin, ozokerite, beeswax, cetyl alcohol, spermacetti and petrolatum in water-in-oil emulsions. In the 1960's, as a consequence of the natural product spermacetti no longer being available, certain of the above-described products could no longer be used, and substitutes had to be created. In 1985, the present inventor introduced stearyl stearate to harden an oil-in-water emulsion system and later commercialized the product under the name Hetester.RTM. 412. Much later, the present inventor worked with the composition behenyl behenate as a possible oil and/or water-in-oil emulsion hardener, but the compound was too waxy and hard and could be utilized effectively only in oil-in-water systems, not water-in-oil systems. The failure of behenyl behenate in water-in-oil emulsion systems started the present inventor on a search for an ester thickener to be used in lieu of paraffin and other natural-type waxes for thickening the oil phase of a water-in-oil emulsion.
Early on in the recent genesis of the instant invention, research centered on the introduction of a liquid emollient dicapryl maleate ("DCM"). With the success of DCM, the next derivative synthesized was a C.sub.12 -C.sub.15 alkyl maleate, which also was a liquid, but had a 0.degree. C. cloud point (the cloud point of DCM is -30.degree. C.). During these research efforts, the present inventor learned that maleate esters will rearrange to fumarate esters, but fumarate esters will not rearrange to maleate esters. Consequently, the present inventor made the C.sub.12 -C.sub.15 fumarate ester, instead of the C.sub.12 -C.sub.15 maleate ester, which unexpectedly produced a solid material which melts at body temperature (about 37-39.degree. C.). That discovery, which provides for a novel emollient composition having favorable melting characteristics at approximately body temperature, is the subject matter of a United States patent application. These products have be en marketed for several years.
In addition to the C.sub.12 -C.sub.15 fumarate ester, C.sub.8, C.sub.16, C.sub.18 and C.sub.20 fumarates have been made with excellent safety, emolliency and other favorable characterisitics. These derivatives, other than the C.sub.8 derivative, have not been marketed to date.
In conducting further research, the present inventor has discovered the highest melting point solid fumaric acid ester (di-behenyl fumarate) which is compatible with high molecular weight oils such as di-octyldodecyl (C.sub.20) fumarate and di-decyltetradecyl (C.sub.24) fumarate. Di-behenyl fumarate has a melting point of about 72-74.degree. C. Utilizing a combination of the di-behenyl fumarate with any cosmetically acceptable emollient oil, the present inventor has d is covered compositions which may be prepared exhibiting a range of viscosity from soft gels to hard sticks, thus providing superior flexibility in formulation. Whether thickening oils only or thickening the oil phase of a water-in-oil emulsion, the resulting combination(s) is (are) uniform in structure, i.e., the di-behenyl fumarate is soluble in the oil phase in all proportions and hardens with equal distribution of the high melting point ester. The result is a uniform, homogeneous product of enhanced stability.